How Aquatic was Spinosaurus?

These days, Spinosaurus is one of the most interesting – and controversial – dinosaurs of all. For a long time, it was only known from a small amount of remains that were described in 1915 and destroyed during a bombing in World War 2. These remains showed that it was a large theropod predator with long spines along its back, but much of the rest of the animal was pure speculation at that point.

Many paleontologists believed the dinosaur’s dorsal spines constituted a kind of sail, like that of the prehistoric synapsid Dimetrodon. Other than the sail, however, most traditional depictions, and even some more modern takes, portrayed Spinosaurus as more or less a standard theropod – large, deep head full of sharp teeth, and a big bulky body with long hind legs and short arms. But many new recent developments have shed some new and challenging light on how we think this dinosaur looked and behaved.

How Big was Spinosaurus?

Even in the early days with little material to go on, it was estimated that Spinosaurus was among the largest theropod dinosaurs of all time. It was believed around that time that Spinosaurus could grow up to 50 feet long or more, though more recent studies have shortened that length a bit.

With new material, scientists have adjusted the size to be smaller than originally thought, though Spinosaurus is still one of the biggest meat-eating dinos ever found. It’s now believed that it measured between 41 and 47 feet long, which puts it right up there with the Tyrannosaurus Rex in terms of length, though it was likely not as heavy bodied.

However, we don’t know exactly how big Spinosaurus was. Though we have more material to help us than scientists did in 1915, it still doesn’t paint a picture of the entire animal, and this is part of what makes this dinosaur so controversial these days.

What did Spinosaurus Look Like?

These days, we do know a bit more about Spinosaurus’s appearance, and it wasn’t just a generic theropod with a sail on its back. We know through skull material discovered in the 1990s and 2000s that Spinosaurus had an elongated, almost crocodile-like snout, which led scientists to believe it likely ate fish.

The skull was similar to other dinosaurs, like Baryonyx and Suchomimus, and paleontologists believe that these and other theropods with similar skulls were all related, and belong in the family Spinosauridae. Some spinosaurids, like Suchomimus, had elongated dorsal spines, but they were nowhere near as extended as those of Spinosaurus. Others, like Baryonyx, had no long back spines to speak of.

 

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Traditional depiction of Spinosaurus Traditional depiction of Spinosaurus

 

Still, for a long time, it was believed that besides the sail, Spinosaurus probably resembled its relatives, with similar proportions and features: longer hindlimbs than forelimbs, a long toothy snout, and a large thumb claw on each of its front limbs. However, this would be challenged by a new description of Spinosaurus in 2014…

What Makes Spinosaurus so Different?

In 2014, newly discovered material was described by paleontologists including Nizar Ibrahim and eight others, which drastically changed how Spinosaurus was viewed, both in its physical form and in the way it was thought to have behaved. While this new description came from the most complete remains yet known of Spinosaurus, it was not without controversy, and many believed (and some still do) that the description must be mistaken.

According to Ibrahim, Spinosaurus was shaped unlike any other dinosaur, with drastically smaller hind legs than anyone had previously believed. This meant that it was likely quadrupedal, walking on four legs most of the time. Before this, it was thought that Spinosaurus was mostly bipedal, usually walking on two legs, and may have occasionally used all four. But this new description changed all that.

Even more shocking, Ibrahim claimed that the shape of Spinosaurus lent itself to an animal that was much more suited for an aquatic lifestyle than a land-based one. It had always been thought that Spinosaurus was suited for catching fish, though most scientists thought it probably stalked the shallows, snatching fish the way a grizzly bear eats salmon. Most paleontologists thought Spinosaurus spent its time around water, but this new description seemed to point to an animal that spent a huge amount of its time submerged in water, and was even an expert swimmer!

 

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Spinosaurus (based on 2014 description)

 

Needless to say, this information did not go over well with many dinosaur fans. While not quite as popular as T-Rex, Spinosaurus was well known enough to be included in movies, books and toy lines, and this revamped interpretation was probably even more provocative than the idea that T-Rex may have had feathers. Many believed it had to be a mistake, and that Ibrahim’s group must have combined skeletons from two or more individuals of different sizes to get such strange and awkward proportions.

Over time, however, people began to mostly accept this new description of Spinosaurus as a swimming, crocodile-like fish eating dinosaur with stumpy hind limbs that moved around on four legs, when it moved around on land at all. So case closed, right? Not quite…

But Wait, There’s More…

A new study by Don Henderson, the curator of dinosaurs at the Royal Tyrrell Museum of Paleontology in Canada, claims that the idea of a deep-diving Spinosaurus would not have been possible. Using computer models, Henderson’s analysis seemed to indicate that Spinosaurus was too top heavy to be an effective swimmer, and would have tipped over on its side easily.

It was also too buoyant to dive, according to Henderson, and couldn’t have sunk its body below the water’s surface. Many other theropod dinosaurs are thought to have been effective floaters, but this new analysis seemed to squash the idea of Spinosaurus as an especially proficient swimmer.

So is that the last word? Not quite. While Henderson’s study opens up the debate about the swimming Spino, it doesn’t close the door. Ibrahim himself has responded to this news, stating that while he’s interested in the new study, he has concerns. For one, digital models like those used by Henderson are not without their flaws, seeing as how it’s not totally possible to create a completely accurate model of an ancient dinosaur known from incomplete remains.

Ibrahim has also stated that Henderson did not base his models on the actual bones used in Ibrahim’s 2014 study. Furthermore, there are still new Spinosaurus remains that have not been formally described, which may shed further light on the topic. “At the end of the day,” Ibrahim says, “the truth lies in the bones, not in a computer.”

So What’s the Verdict? Was Spinosaurus a Good Swimmer or Not?

Ultimately, what it comes down to is this - what we know about dinosaurs is rapidly changing, and any understanding we have is always vulnerable to change if more complete remains are discovered.

What do we know? We know that Spinosaurs ate fish, due to scales found in stomach contents. We know Spinosaur remains are often found in areas that were home to coastal areass and rivers in the distant past. We also know that Spinosaur jaws and teeth were uniquely suited for a diet of fish. And, perhaps most important of all, certain chemical isotopes uncovered in Spinosaur remains seem to indicate that much of their time was spent in the water, rather than on land.

Despite the initial controversy around the radically new body shape suggested by Ibrahim’s description, most paleontologists today seem to accept that Spinosaurus was more similar to the animal he and his colleagues described than the traditional depiction of the dinosaur. Henderson’s model, while it does challenge the idea of Spinosaurus as a powerful swimmer, does not challenge the basic body plan put forth in the 2014 study.

We do know that Spinosaurus relied on a diet of fish and spent a lot of time near the water, but what remains a mystery is exactly how suited it was for the water. Did it stalk the water’s edge like a grizzly bear, or wade into the water like a heron, or swim after prey like a crocodile? Henderson’s study, while interesting, is far from the final say on this issue. As more bones of Spinosaurus are formally described, a more complete picture of this unique and fascinating theropod fish-eater will be revealed. In the meantime, we can only give our best guesses based on the material available to us.

 

 

 

 

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